The present invention relates to a slim switch which is employed in operation areas of various apparatuses such as electrical appliances.
A membrane switch, for example, is known as the slim switch. This membrane switch is employed in operation areas of various apparatuses such as electric appliances, because it is highly reliable and contributes to realization of space saving.
In FIG. 3, a membrane switch 51 comprises an exterior sheet 52, a spacer sheet 53 and a circuitry 54, which are laminated on a base plate 55. The respective members are bonded with each other with adhesive layers 56.
A movable contact 57 is provided on a predetermined position of a back face of the exterior sheet 52. A through hole 58 is formed in the spacer sheet 53 in alignment with the position of the movable contact 57. The circuitry 54 is provided with a switch circuit having an appropriate pattern, which is not shown. Fixed contacts 59 are provided on the switch circuit at positions opposed to the movable contact 57.
In the membrane switch 51 having the above described structure, when a front face of the exterior sheet 52 is pressed downward with switch operation of a finger 60 of an operator, as shown by an arrow mark, the movable contact 57 and the fixed contacts 59 are brought into electrical contact with each other in association with flexure of the exterior sheet 52. In this manner, the conductive condition of the non-shown switch circuit is established. On the other hand, when the finger 60 of the operator is detached from the membrane switch 51, the exterior sheet 52 which is flexed until then will be recovered to the original state, and the conductive condition of the switch circuit will be released.
Besides the above described membrane switch 51, a dome switch having the following structure is commonly used as the slim switch.
In FIGS. 4 and 5, a dome switch 61 comprises an exterior sheet 62, a spacer sheet 63 and a circuitry 64 which are laminated on a base plate 65. The respective members are bonded to each other with adhesive layers 66. Moreover, the dome switch 61 is designed in such a manner that more improved feeling of click as compared with the above described membrane switch 51 (see FIG. 3) can be obtained.
The exterior sheet 62 is formed with a dome part 67 which is projected in a dome shape. A movable contact 68 is provided at the top of a back face of the dome part 67. A through hole 69 is formed in the spacer sheet 63 at a position corresponding to the dome part 67. Into this through hole 69, the dome part 67 which is projected downward is adapted to be inserted. The circuitry 64 is provided with a not-shown switch circuit with an appropriate pattern. Fixed contacts 70 are provided on the switch circuit at positions opposed to the movable contact 68.
In the dome switch 61 having the above described structure, when the dome part 67 is pressed downward with switch operation of a finger 71 of an operator as shown by an arrow mark, and the movable contact 68 of the dome part 67 which is projected downward comes into electrical contact with the fixed contacts 70 of the circuitry 64, the conductive condition of the non-shown switch circuit can be obtained. When the dome part 67 is projected downward, the feeling of click can be obtained. On the other hand, when the finger 71 of the operator is detached from the dome part 67, the dome part 67 which is projected downward until then will be recovered to the original state, and the conductive condition of the non-shown switch circuit will be released.
The above described membrane switch 51 and the dome switch 61 have had several problems as follows.
First, there is a problem that it is difficult to secure a sufficient stroke length when the switch is operated. There is such an anxiety that a person who operates the switch is unable to reliably recognize ON-OFF of the switch.
Second, there is a problem that operation load of the switch operation is determined to some extent, depending on a shape of the part to be pressed, and it is actually difficult to change feeling of the switch operation even if so desired. Third, there is another problem that freeness of design is limited due to the shape of the part to be pressed.
Lastly, in the dome switch 61, when the dome part 67 which is projected downward is recovered to the original state, speed of the recovery may be faster than speed of the finger 71 to be detached. Therefore, there is a problem that some of the operators may feel uncomfortable when they receive a repulsive force of the dome part 67.
It is therefore an object of the invention to provide a slim switch in which a sufficient stroke length at the switch operation can be secured, and improved feeling of the switch operation can be obtained. It is also an object of the invention to provide a slim switch in which freeness of design can be enhanced.
In order to achieve the above object, according to the invention, there is provided a switch, comprising:
a circuitry, provided with a first switching contact;
a first spacer, laminated on the circuitry so as to provide a first space above the first switching contact;
a first, elastic sheet member, laminated on the first spacer and provided with a second switching contact opposing to the first switching contact in the first space, the first sheet member being operable to deform while using the first space to bring the second switching contact into an electrical contact with the first switching contact;
a second spacer, laminated on the first sheet member so as to provide a second space above a first part of the first sheet member;
a second sheet member, laminated on the second spacer, the second sheet member being operable to deform while using the second space to thereby deform the first part of the first sheet member; and
an elastic member, interposed between the first sheet member and the second sheet member at the second space, the elastic member having an elastic deformability which is higher than an elastic deformability of the first sheet member.
In such a configuration, when the switch is operated, the second sheet member is first subjected to a pressure load and deformed, and at the same time, the elastic member is elastically deformed. Then, the first part of the first sheet member is deformed downward, so that the second switching contact is brought into contact with the first switching contact. With this action, the switch is turned on. On the other hand, when the pressure load is released, the first part of the first sheet member deformed downward, the elastic member elastically deformed, and the second sheet member deformed downward are recovered to their original state, and the conductive condition of the switch is released. On this occasion, a repulsive force of the first part of the first sheet member is absorbed by the elastic member.
Accordingly, not only a sufficient stroke length can be secured, but also the freeness of design of the second sheet member serving as an exterior appearance member can be enhanced. Further, the feeling at the switch operation can be improved.
Preferably, the static member is fixed to at least one of faces of the first sheet member and the second sheet member which are opposed to each other through the second space.
In such a configuration, since distance between the first sheet member and the second sheet member is kept constant, the stroke length can be always secured in a stabilized state. Moreover, the feeling at the switch operation can be maintained in a favorable condition.
Preferably, the first part of the first sheet member is projected toward the second sheet member in a condition where no load is applied thereto.